As I understand it, Anaconda installs from the newest available packages when doing the initial install. So there's no value to having deltarpm support available early on, since Anaconda won't do updates, it'll just install from the latest. If this is a feature that's important to you, I'd suggest installing it in your kickstart, or immediately after install. As long as it's in place before you run your first 'yum update,' you get the bandwidth gains.
There are probably lots of small utilities that would be useful in a minimal install, but that way lies bloat. I also assume we're tracking upstream's minimal install, so CentOS is rather limited in what it can add without diverging too far.